Think of it as "why can't quant traders trade systematically", sort of a FizzBuzz for quant traders. If you're not familiar with FizzBuzz, read about it here: https://blog.codinghorror.com/why-cant- ... s-program/

So you're a quant trader with 10s of years of experience in the industry and a job title like "head of quant trading desk" (seen around here) or some other quant type who rants about things like "market making is boring" (seen on Nuclear Phynance). You're interviewing other wannabe quant traders or yourself are getting interviewed (likely questions of the like "approximate exp(5) with two decimals on paper").

Here's my test:

1) Do you have $10k - $1M of your own savings?
2) Can you open a personal account on Interactive Brokers and fund it with those $10k - $1M as trading capital?
3) Using Interactive Brokers's API, can you implement a (set of) systematic trading strategy(es) that allow you, *personally*, to live off it?

If the answer to any of the 1-3 is negative then:
a) If you're looking for a job then you're a no-hire.
b) If you're already having a job then do your best to hold on to it, because #a.

I'm willing to bet that 99% of the "quant traders" (either looking for a job or already employed) would fail the test. Which makes me wonder what the funk 99% of this industry is about since it's not about making money.

yes, I agree that close to 100% traders (of any sort) would fail that test. 

I assume your last sentence poses a rhetorical question, but if not, 
here is a good answer from Warren Buffet